1. Field of the Invention
The present invention is directed generally to printing duplex and simplex copy sheets from electronic page information, especially suitable for low cost electrostatographic, ink jet, ionographic or other on-demand page printers with an endless duplex paper path loop. More particularly, the present invention relates to such printers which are integrated with on-line finishing devices which cannot immediately receive copy sheets from a subsequent set when performing its finishing operations on a current set of copy sheets (i.e., finishing devices which require an interset interval so that a first set is sufficiently cleared out of the way for the finishing device to begin receiving sheets from a second, subsequent set).
2. Description of Related Art
The terminology "copiers", and "copies", as well as "printers" and "prints", is used alternatively herein. The terminology "imaging" and "marking" is used alternatively herein and refers to the entire process of putting an image (digital or analog source) onto paper. The image can then be permanently fixed to the paper by fusing, drying, or other means. It will be appreciated that the invention may apply to almost any system in which the images are made electronically, including electronic copiers.
Imaging systems (e.g., printers or copiers) typically include copy sheet paper paths through which copy sheets (e.g., plain paper) which are to receive an image are conveyed and imaged. The process of inserting copy sheets into the copy sheet paper path and controlling the movement of the copy sheets through the paper path to receive an image on one or both sides, is referred to as "scheduling". Copy sheets are printed by being passed through a copy sheet paper path (which includes a marking station) one or multiple times. Copy sheets which are printed on only one side (simplex copy sheets) in a single color usually pass through the copy sheet paper path a single time. Multipass printing is used to print images on both sides of a copy sheet (duplex printing), or to print a simplex sheet in multiple colors (one pass for each color). There are two general modes in which copy sheets to be multipass printed can be scheduled: "burst mode" and "interleave mode".
When scheduling in "burst mode", copy sheets are inserted into, imaged, and output from the copy sheet paper path without any "skipped pitches" existing between each consecutive copy sheet. A "pitch" is the portion (or length) of the copy sheet paper path in the process direction which is occupied by a copy sheet as it moves through the copy sheet paper path. A "skipped pitch" occurs when there is a space between two consecutively output copy sheets which is long enough to hold another copy sheet. Accordingly, when scheduling in "burst mode", copy sheets are output from the copy sheet paper path (and, thus, the imaging system) at a maximum rate because no skipped pitches exist between each consecutively output copy sheet.
Various methods for scheduling copy sheets in "burst mode" are disclosed in, for example, the above incorporated U.S. Pat. application No. 07/590,236.
When scheduling copy sheets in "interleave mode", skipped pitches are provided between each consecutively scheduled copy sheet. That is, a space is provided between each copy sheet inserted into and output from the copy sheet paper path. While other copy sheets eventually may be inserted in the space between two consecutively input copy sheets, these other copy sheets are inserted at a later time (described below) and are thus "interleaved" with the previously input copy sheets.
This "interleave mode" of copy sheet scheduling is typically employed in imaging systems which are capable of duplex printing (forming images on both sides of a copy sheet). Many imaging systems which are capable of duplex printing include copy sheet paper paths in the shape of a loop. The scheduling process involves: a) inserting a copy sheet into the loop; b) forming an image on a first side of the copy sheet at an imaging station; c) inverting the copy sheet (so that a second side of the copy sheet will face the imaging station when the copy sheet is reconveyed past the imaging station); d) forming an image on the second side of the copy sheet at the imaging station; and e) outputting the copy sheet from the paper path loop toward a final destination (a tray, a bindexer, finishing devices, etc.).
One reason why the "interleave mode" of scheduling is frequently used when duplex printing relates to the manner in which the original images are provided to the imaging station. For example, when the imaging system is using a recirculating document handler (RDH) to cycle a simplex document over a platen for exposure to a light source for forming duplex copies of the document, the imaging system exposes every other sheet in the simplex document so that a duplex copy of the document can be formed. For example, all even numbered pages in the document are exposed first to form a copy set consisting of copy sheets having even numbered pages on one side. Then, the odd numbered pages in the document are exposed, and these odd numbered pages are formed on the second side of the copy sheets containing the even numbered pages on side one.
The Xerox Corporation "9700" printer, duplex version, is an example of a printer having a long duplex paper path loop and which schedules copy sheets in the interleave mode of operation. It operates in essentially a trayless mode, with a long duplex loop path. Initially, prints (copies) of only the even sides are made, with one skip cycle (skipped pitch) between each print until the entire paper path is filled with even side prints alternated with skipped pitches. When the first completed even side (page 2) reaches the transfer area for the second side print (page 1), that page is printed on the back side. The next print to be made, however, is the next even side in the sequence printed on a blank sheet, and interleaved in the blank spaces (previously skipped pitches) left between sheets on the first pass. Thus, the job then proceeds at full productivity, intermixing (or interleaving) even sides printed on blank sheets for the first pass with odd sides printed on the back of previously completed even sides on their second pass. After the last even side is printed, the system resumes the skip pitch operation until the odd sides are printed on the last of the even side prints.
For a 30 page job, this "9700" printer duplex version page copying sequence can be represented as shown below. [Each "S" represents a skipped pitch. Previously printed sheet pages making their second pass for their second side copy are shown under the slash.]
First stage--[evens copied+skips=half productivity]:
2, S, 4, S, 6, S, 8; PA1 1/2, 10, 3/4, 12, 5/6, 14, 7/8, 16, 9/10, 18, 11/12, 20, 13/14, 22, 15/16, 24, 17/18, 26, 19/20, 28, 21/22, 30; PA1 23/24, S, 25/26, S, 27/28, S, 29/30.
Second stage--[odds and evens intermixed--full productivity]:
Third stage--[odds copied+skips=half productivity];
Note that with this "9700" printer sequence, 36 machine pitches are required to make 30 prints. So, for this 30 page job, the overall duplex operation is only 83% efficient. For longer jobs, the effective efficiency improves. But for shorter jobs the overall efficiency degrades, since there will still be 6 skipped pitches--"S".
The sequence used on Xerox Corporation "5700" printer is somewhat similar, except that it is not a trayless duplex loop system. All the completed first side sheets are stacked into a duplex buffer tray and later refed for side two printing. With this system, printer skipped pitches are not required during the first stage of the job. The skipped pitches are also not required for the third stage since the completed side ones can be fed at full thruput from the duplex tray. Thus, the "5700" duplexing is much more efficient than in the "9700". However, such duplex tray systems are inherently less reliable in some respects. The required duplex tray stacking, reseparating, and refeeding is implicated in the vast majority of duplex paper jams, and complicates job recovery. That is eliminated with the "9700" and other endless moving path duplex buffer loop systems.
Other conventional sequences for printers are also possible. For example, the Hewlett Packard HP "2000" uses a stack and re-feed method of duplex in which all even sides of the entire job are printed, followed by printing all of the odd sides. However, for this, the entire job (all the page images) must be stored in memory in order to insure jam recovery.
It is generally known that electronically inputted printers can desirably provide more flexibility in page sequencing (page, copying presentation order) than copiers with physical document sheet input. The printer input is electronically manipulatable electronic page media, rather than physical sheets of paper which are much more difficult to reorder or manipulate into a desired sequence. As also shown in the art noted hereinbelow, it is generally known that certain such reordered or hybrid document page copying orders or sequences may be copied onto a corresponding sequential train of copy sheets in an appropriate copier or printer to provide higher copying machine productivity yet correct page order copy output, especially for duplex copies made with a copier with trayless duplexing, i.e., providing a limited length endless buffer loop duplexing path for the copy sheets being duplexed.
Thus, electronically inputted imaging systems can operate in "burst mode" even when forming duplex copy sets. When operating in burst mode in an electronically inputted imaging system having an endless buffer loop duplexing paper path (no buffer tray), the duplexing paper path is completely filled with copy sheets (no skipped pitches) which are then imaged on both sides before being output from the duplexing paper path. Duplex burst mode scheduling causes duplex sheets to be output in small bursts of sheets (the duplex loop content) at full rated output.
When printing multiple sets of copy sheets which contain at least some duplex printed copy sheets in burst mode or interleave mode, in certain situations, it is possible to intermix the copy sheets from different sets or jobs as long as the order in which the sets are output from the duplex paper path (and the final destinations of each set) does not result in the output printed sets being intermixed. A number of scheduling algorithms for increasing printer productivity by intermixing copy sheets are disclosed in the above incorporated U.S. Pat. application Ser. No. 07/590,236. These algorithms operate locally in that they determine whether to insert a copy sheet from a supply bin into the duplex paper path based upon information that is available when the copy sheet is to be inserted into the duplex paper path. Although the algorithms disclosed in U.S. Pat. No. 07/590,236 are used to schedule copy sheets in burst mode, there are situations, described, for example, in the above incorporated U.S. Pat. application No. 07/752,108 (Attorney Docket No. JAO 26716), where it is desirable to schedule copy sheets in interleave mode. The same algorithms can be used to schedule copy sheets in interleave mode as in burst mode, with one additional constraint on pitch availability at the point of copy sheet insertion: a pitch of the duplex path is unavailable (to receive a new sheet from the supply bin) if a side one or a simplex sheet was scheduled in the preceding pitch.
The present invention is applicable to burst mode or interleave mode scheduling, performed as described above, or using other logic which results in similar copy sheet output (no skipped pitches between consecutively output copy sheets or a skipped pitch between at least some of the consecutively output copy sheets).
It is becoming increasingly common to integrate on-line finishing devices with imaging systems. These on-line finishing devices directly receive copy sheets as they are output from the imaging system and perform various types of finishing operations on each copy sheet, or on each set of copy sheets. The finishing operations can be, for example: binding, stitching, folding, trimming, aligning, rotating, punching, drilling, slitting, perforating, and combinations thereof.
Problems can arise when integrating an existing finishing device with a high speed imaging system. For example, the finishing device may not be able to immediately receive copy sheets output by the imaging system from a subsequent set (a second set) when it is performing its finishing operation(s) on the preceding set (a first set).
Typically, an appropriate number of skipped pitches are scheduled between the last copy sheet in the first set and the first copy sheet in the next (second) set so that a sufficient amount of time exists for the finishing device to perform its finishing operation on the first set before the first printed copy sheet from the second set reaches the finishing device. The appropriate number of skipped pitches is referred to as the "interset interval". The length of the interset interval (in pitches) can vary depending on the pitch mode (or more precisely, the sheet delivery interval) and the number of copy sheets in each set of copy sheets. When the finishing task is distributed among multiple operations and/or modules, the interset interval must be sufficient to prevent a subsequent set from overtaking the current set in each module.
Table 1 illustrates some examples of scheduling which includes providing interset intervals between the output of each set of copy sheets. In these examples, the duplex paper path loop length is 8 pitches, each set is 6 sheets long, and the interset interval is 3 pitches. The interset interval scheduling operated as follows:
A) if the first set is simplex, insert the interset interval (3) skipped pitches after the pitch containing the last side one image of the first set;
B) if the first set is duplex, insert the interset interval (3) skipped pitches after the pitch reserved for the side two image of the last sheet in the first set if the next set is simplex, otherwise, if the next set is duplex, insert the interset interval (3) skipped pitches after the pitch containing the side one image of the last sheet in the first set.
TABLE 1 __________________________________________________________________________ A B C D Simplex to Simplex to Duplex to Duplex to Pitch Simplex Duplex Simplex Duplex __________________________________________________________________________ 1 set 1, sheet 1 set 1, sheet 1 set 1, side 1, sheet 1 set 1, side 1, sheet 1 2 set 1, sheet 2 set 1, sheet 2 set 1, side 1, sheet 2 set 1, side 1, sheet 2 3 set 1, sheet 3 set 1, sheet 3 set 1, side 1, sheet 3 set 1, side 1, sheet 3 4 set 1, sheet 4 set 1, sheet 4 set 1, side 1, sheet 4 set 1, side 1, sheet 4 5 set 1, sheet 5 set 1, sheet 5 set 1, side 1, sheet 5 set 1, side 1, sheet 5 6 set 1, sheet 6 set 1, sheet 6 set 1, side 1, sheet 6 set 1, side 1, sheet 6 7 skip skip skip 8 skip skip skip 9 skip skip set 1, side 2, sheet 1 set 1, side 2, sheet 1 10 set 2, sheet 1 set 2, side 1, sheet 1 set 1, side 2, sheet 2 set 1, side 2, sheet 2 11 set 2, sheet 2 set 2, side 1, sheet 2 set 1, side 2, sheet 3 set 1, side 2, sheet 3 12 set 2, sheet 3 set 2, side 1, sheet 3 set 1, side 2, sheet 4 set 1, side 2, sheet 4 13 set 2, sheet 4 set 2, side 1, sheet 4 set 1, side 2, sheet 5 set 1, side 2, sheet 5 14 set 2, sheet 5 set 2, side 1, sheet 5 set 1, side 2, sheet 6 set 1, side 2, sheet 6 15 set 2, sheet 6 set 2, side 1, sheet 6 skip skip 16 skip skip set 2, side 1, sheet 1 17 skip skip set 2, side 1, sheet 2 18 skip set 2, side 2, sheet 1 set 2, sheet 1 set 2, side 1, sheet 3 19 set 3, sheet 1 set 2, side 2, sheet 2 set 2, sheet 2 set 2, side 1, sheet 4 20 set 3, sheet 2 set 2, side 2, sheet 3 set 2, sheet 3 set 2, side 1, sheet 5 21 set 3, sheet 3 set 2, side 2, sheet 4 set 2, sheet 4 set 2, side 1, sheet 6 22 set 3, sheet 4 set 2, side 2, sheet 5 set 2, sheet 5 23 set 3, sheet 5 set 2, side 2, sheet 6 set 2, sheet 6 24 set 3, sheet 6 set 2, side 2, sheet 1 __________________________________________________________________________
The skipped pitches which are inserted to provide the 3 pitch interset interval are labelled "skip". Unlabeled pitches (column B, pitches 16 and 17; column C, pitches 7 and 8; oolumn D, pitches 22 and 23) are gaps which naturally occur due to duplex scheduling and the feature of buffer-trayless duplex paper paths that each copy sheet remains in the same pitch of the paper path for receiving its side two image. Also note that pitches 7 and 8 in column D, are counted as skipped pitches for the interset interval, and also occur naturally as a result of duplex scheduling.
It is not desirable to schedule skipped pitches if they are not necessary because they cause a decrease in productivity.
Accordingly, there is a need for an imaging system which optimizes copy sheet output productivity while providing an appropriate interset interval between output sets of printed copy sheets that are destined for on-line finishing devices used therewith.
U.S. Pat. No. 4,918,490 to Denis J. Stemmle (Xerox Corporation) discloses an endless duplex paper path loop having a single sheet inverter for inverting sheets in the duplex loop after side one imaging. Sheets are consecutively inserted into the duplex loop to avoid the first and third stage skipped pitches discussed above with reference to the "9700" system. Sheets are scheduled in 1-N order, with each multipage job set being electronically divided into consecutive batches, each batch containing a small number of pages equal to approximately twice the copy sheet length.
Also of interest is Mead Corporation U.S. Pat. No. 4,453,841 issued Jun. 12, 1984 to Bobick et al disclosing a trayless duplexing buffer loop path printer system, and noting particularly the page copying sequences shown in FIG. 6.
Some examples of other prior art printers, and especially with control systems therefor, including operator console switch selection inputs, document sheet detecting switches, etc., are disclosed in U.S. Pat. Nos.: 4,054,380; 4,062,061; 4,076,408; 4,078,787; 4,099,860; 4,125,325; 4,132,401; 4,144,550; 4,158,500; 4,176,945; 4,179,215; 4,229,101; 4,278,344; 4,284,270; and 4,475,156. It is well known in this art, and in general, how to program and execute document handler and printer control functions and logic with conventional or simple software instructions for conventional microprocessors in a printer controller. This is taught by the above and other patents and various commercial copiers/printers. Such software may vary depending on the particular function and particular microprocessor or microcomputer system utilized, of course, but will be available to or readily programmable by those skilled in the applicable arts without undue experimentation, from either descriptions or prior knowledge of the desired functions together with general knowledge in the general software and computer arts. It is also known that conventional or specified document and copy sheet handling functions and controls may be alternatively conventionally provided utilizing various other known or suitable logic or switching systems.
All references cited in this specification, and their references, are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.